Upon DNA damage, histone modifications are dynamically reshaped to accommodate DNA damage signaling and repair within chromatin. In this study, we report the identification of the histone demethylase KDM5A as a key regulator of the bromodomain protein ZMYND8 and NuRD (nucleosome remodeling and histone deacetylation) complex in the DNA damage response. We observe KDM5A-dependent H3K4me3 demethylation within chromatin near DNA double-strand break (DSB) sites. Mechanistically, demethylation of H3K4me3 is required for ZMYND8–NuRD binding to chromatin and recruitment to DNA damage. Functionally, KDM5A deficiency results in impaired transcriptional silencing and repair of DSBs by homologous recombination. Thus, this study identifies a crucial function for KDM5A in demethylating H3K4 to allow ZMYND8–NuRD to operate within damaged chromatin to repair DSBs.